Wireless communication apparatus, wireless communication method, and program

ABSTRACT

To make it possible to perform retransmission control in which wireless resources are more efficiently utilized, a wireless communication apparatus includes: a wireless communication unit configured to perform wireless communication with a terminal apparatus; a communication control unit configured to control multicast transmission performed by the wireless communication unit; and a setting unit configured to set a threshold for determining whether or not it is necessary for the communication control unit to perform a retransmission process, on the basis of information about reception of a reception acknowledgment response corresponding to the multicast transmission from the terminal apparatus.

TECHNICAL FIELD

The present disclosure relates to wireless communication apparatuses,wireless communication methods, and programs.

BACKGROUND ART

Among the communication techniques in wireless systems is multicastcommunication. Multicast communication is a communication technique oftransmitting a single piece of data to one or more wireless terminalsbelonging to a multicast group as transmission destinationssimultaneously. Multicast communication allows for efficient utilizationof wireless resources, and therefore, is employed in various services,and there is a demand for an improvement in techniques related tomulticast communication.

For example, Patent Literature 1 below discloses a technique of, whendata has been transmitted using multicast communication, determiningwhether or not to perform retransmission on the basis of whether or notthe number of terminals which are transmission destinations is equal tothe number of reception acknowledgment responses received from terminalswhich are transmission destinations.

CITATION LIST Patent Literature

-   Patent Literature 1: JP H11-17713A

SUMMARY OF INVENTION Technical Problem

According to the above technique disclosed in the Patent Literature 1,retransmission is performed until a reception acknowledgment responsehas been received from all terminals that are multicast transmissiondestinations. However, in wireless communication, if retransmission isrepeatedly performed until a reception acknowledgment response has beenreceived from all terminals, retransmission is more frequently performedas the number of wireless terminals belonging to a multicast groupincreases, so that wireless resources are infinitely consumed. As denserwireless networks are being currently constructed, it is desirable thatsuch a waste of wireless resources should be avoided. With this in mind,the present disclosure proposes a novel and improved wirelesscommunication apparatus, wireless communication method, and programwhich can perform retransmission control in which wireless resources aremore efficiently utilized.

Solution to Problem

According to the present disclosure, there is provided a wirelesscommunication apparatus including: a wireless communication unitconfigured to perform wireless communication with a terminal apparatus;a communication control unit configured to control multicasttransmission performed by the wireless communication unit; and a settingunit configured to set a threshold for determining whether or not it isnecessary for the communication control unit to perform a retransmissionprocess, on the basis of information about reception of a receptionacknowledgment response corresponding to the multicast transmission fromthe terminal apparatus.

According to the present disclosure, there is provided a wirelesscommunication method for use in a wireless communication apparatus whichperforms wireless communication with a terminal apparatus, the methodincluding: controlling multicast transmission using a processor; andsetting a threshold for determining whether or not it is necessary toperform a retransmission process, on the basis of information aboutreception of a reception acknowledgment response corresponding to themulticast transmission from the terminal apparatus.

According to the present disclosure, there is provided a program forcausing a computer to function as: a wireless communication unitconfigured to perform wireless communication with a terminal apparatus;a communication control unit configured to control multicasttransmission performed by the wireless communication unit; and a settingunit configured to set a threshold for determining whether or not it isnecessary for the communication control unit to perform a retransmissionprocess, on the basis of information about reception of a receptionacknowledgment response corresponding to the multicast transmission fromthe terminal apparatus.

Advantageous Effects of Invention

As described above, according to the present disclosure, retransmissioncontrol in which wireless resources are more efficiently utilized can beperformed. Note that the effects described above are not necessarilylimitative. With or in the place of the above effects, there may beachieved any one of the effects described in this specification or othereffects that may be grasped from this specification.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an illustrative diagram for describing an overview of acommunication system according to a first embodiment.

FIG. 2 is a block diagram showing a logical configuration example of abase station according to the first embodiment.

FIG. 3 is a flowchart showing a flow example of a retransmission processperformed in a base station according to the first embodiment.

FIG. 4 is a flowchart showing a flow example of a threshold settingprocess performed in a base station according to the first embodiment.

FIG. 5 is a flowchart showing a flow example of a retransmission methoddetermination process performed in a base station according to the firstembodiment.

FIG. 6 is a flowchart showing a flow example of a retransmission timingdetermination process performed in a base station according to the firstembodiment.

FIG. 7 is a flowchart showing a flow example of a threshold settingprocess performed in a base station according to Variation 1.

FIG. 8 is a flowchart showing a flow example of a threshold settingprocess performed in a base station according to Variation 2.

FIG. 9 is a flowchart showing a flow example of a retransmission processperformed in a base station according to a second embodiment.

FIG. 10 is a block diagram showing a schematic configuration example ofa wireless access point.

DESCRIPTION OF EMBODIMENT(S)

Hereinafter, (a) preferred embodiment(s) of the present disclosure willbe described in detail with reference to the appended drawings. In thisspecification and the appended drawings, structural elements that havesubstantially the same function and structure are denoted with the samereference numerals, and repeated explanation of these structuralelements is omitted.

Also, in the present specification and drawings, elements havingsubstantially the same functional configuration may be distinguishedfrom each other by adding different letters of the alphabet to the samereference sign. For example, a plurality of elements havingsubstantially the same functional configuration are distinguished fromeach other when necessary, like wireless terminals 200A, 200B, and 200C.Note that when it is not necessary to particularly distinguish aplurality of elements having substantially the same functionalconfiguration from each other, the elements are denoted by only the samereference sign. For example, when it is not necessary to particularlydistinguish wireless terminals 200A, 200B, and 200C from each other, thewireless terminals 200A, 200B, and 200C are simply referred to as thewireless terminals 200.

Note that description will be provided in the following order.

1. Introduction 2. First Embodiment

2-1. Overview of communication system2-2. Configuration examples of base station2-3. Operation process examples

2-4. Variation 1 2-5. Variation 2 3. Second Embodiment

3-1. Configuration examples of base station3-2. Operation process examples4. Application examples

5. Conclusion 1. Introduction

Firstly, techniques and discussions related to multicast communicationwill be described.

(Communication Techniques)

Communication techniques in wireless systems include, for example,unicast communication, multicast communication, and broadcastcommunication. These communication techniques are employed forcommunication between a base station and a terminal device in, forexample, a wireless local area network (LAN) system. Note that theterminal device is a wireless terminal connected to a base station.

Unicast Communication

Unicast communication is a communication technique used in one-to-onedata transmission. For example, unicast communication is used when abase station transmits data to a single terminal device. However, inunicast communication, for example, when a base station transmits thesame data to a plurality of terminal devices, a frame is transmitted toterminal devices separately, and therefore, the efficiency ofutilization of wireless resources is low. Meanwhile, in unicastcommunication, if a protocol is specified so that a receptionacknowledgement request is transmitted to each terminal device, and areception acknowledgment response (ACK) is received from a terminaldevice which has succeeded in reception, retransmission is performedwith respect to a terminal device which has failed to receive a frame sothat frame dropping can be reduced. Note that a frame transmitted usingunicast communication is also referred to as a unicast frame. Also, totransmit a unicast frame is also referred to as unicast transmission.

Multicast Communication

Multicast communication is a communication technique used in one-to-manydata transmission. For example, multicast communication is used when abase station transmits the same data to one or more terminal devicesbelonging to a predetermined group. This group is also referred to as amulticast group. In multicast communication, a single piece of data canbe transmitted to a plurality of terminal devices simultaneously.Therefore, the efficiency of utilization of wireless resources is higherin multicast communication than in unicast communication. Note that atypical wireless communication system is not provided with a mechanismfor performing retransmission of a frame which has been transmittedusing multicast communication, and therefore, it is difficult to reduceframe dropping. Note that a frame transmitted using multicastcommunication is also referred to as a multicast frame. Also, totransmit a multicast frame is also referred to as multicasttransmission.

Broadcast Communication

Broadcast communication is a communication technique used in one-to-manydata transmission. For example, broadcast communication is used when abase station transmits the same data to all wireless terminals presentwithin a range in which a frame transmitted from the base station can besensed. Broadcast communication is typically used for transmission of abeacon frame which is used when a base station notifies of its presence,or the like.

In the foregoing, each communication technique in a wireless system hasbeen described.

(Retransmission Control in Multicast Communication)

As a mechanism for retransmission control involved in multicastcommunication, a mechanism for performing retransmission until areception acknowledgment response has been received from all terminaldevices belonging to a multi cast group, is conceived of. However, whena transmitter repeatedly performs retransmission until a receptionacknowledgment response has been received from all terminal devices,retransmission is more frequently performed as the number of terminaldevices belonging to a multicast group increases, so that wirelessresources are infinitely consumed.

With this in mind, in each embodiment of the present disclosure, amechanism is provided in which when a reception acknowledgment responsehas been received from a portion of the terminal devices belonging to amulticast group, it is assumed that multicast transmission has beensuccessful, and retransmission will not be performed. Specifically, inthis embodiment, a threshold is introduced in order to determine whetheror not multicast transmission has been successful. As a result, thenumber of times of retransmission and the number of times oftransmission of a reception acknowledgment response accompanyingretransmission, can be reduced. Furthermore, in this embodiment, byintroducing a mechanism for dynamically changing this threshold, moreefficient utilization of wireless resources is achieved. Also, in thisembodiment, a retransmission method and a retransmission timing aredetermined, depending on a terminal device requiring retransmission,whereby retransmission can be more efficiently performed.

Thus, according to each embodiment of the present disclosure, the numberof times of retransmission, and the number of times of transmission of areception acknowledgment response accompanying retransmission, arereduced, and in addition, retransmission is performed using a moreappropriate retransmission method and retransmission timing. As aresult, an improvement in efficiency of utilization of wirelessresources in multicast communication and an improvement in systemthroughput are achieved.

2. First Embodiment [2-1. Overview of Communication System]

Firstly, an overview of a communication system according to thisembodiment will be described with reference to FIG. 1.

FIG. 1 is an illustrative diagram for describing the overview of thecommunication system according to this embodiment. As shown in FIG. 1,the communication system 1 includes a base station 100 and a pluralityof wireless terminals 200 (i.e., wireless terminals 200A, 200B, 200C,200D, 200E, and 20F). The communication system 1 is, for example, asystem compliant with wireless LAN or a communication technique similarto this.

The base station 100 is a wireless communication apparatus correspondingto a base device which is a center of the communication system 1. Thebase station 100 may be connected to an external network, such as theInternet or the like, by wire or wirelessly. For example, the basestation 100 may be an access point in a wireless LAN system.

The wireless terminals 200 are each a wireless communication apparatuscorresponding to a terminal device which is wirelessly connected to thebase station 100 for communication. In FIG. 1, dashed lines indicatethat the wireless terminals 200 are wirelessly connected to the basestation 100. For example, the wireless terminals 200 may be a station ina wireless LAN system.

It is hereinafter assumed that the wireless terminal 200A to 200F belongto the same multicast group. Needless to say, not all of the wirelessterminals 200 wirelessly connected to the base station 100 may belong tothe same multicast group.

The base station 100 performs multicast communication. Specifically, thebase station 100 transmits the same multicast frame to the wirelessterminals 200A to 200F belonging to the same multicast group.

A wireless terminal 200 which has succeeded in receiving a multicastframe transmits a reception acknowledgment response (ACK frame) back tothe base station 100. The wireless terminals 200 may transmit areception acknowledgment response back at different timings or in atime-division multiplexing manner. Also, the base station 100 mayexplicitly request the wireless terminals 200 within the coveragethereof to transmit an ACK frame back.

The base station 100 performs retransmission control on a frame whichhas been transmitted using multicast communication, on the basis ofinformation about reception of an ACK frame transmitted back from awireless terminal 200.

In the foregoing, an overview of the communication system 1 according tothis embodiment has been described. Next, a configuration example of thebase station 100 according to this embodiment will be described withreference to FIG. 2.

[2-2. Configuration Examples of Base Station]

FIG. 2 is a block diagram showing a logical configuration example of thebase station 100 according to this embodiment. As shown in FIG. 2, thebase station 100 has a wireless communication unit 110, a storage unit120, and a control unit 130.

(1) Wireless Communication Unit 110

The wireless communication unit 110 is a wireless communicationinterface which mediates wireless communication of the base station 100with other devices. In this embodiment, the wireless communication unit110 performs wireless communication with the wireless terminals 200. Forexample, the wireless communication unit 110 receives wireless signalstransmitted from the wireless terminals 200. The wireless communicationunit 110 may function as, for example, an amplifier, frequencyconverter, demodulator, or the like, and output received data to thecontrol unit 130. Also, the wireless communication unit 110 transmits awireless signal to the wireless terminals 200 through an antenna. Thewireless communication unit 110 may function as, for example, amodulator, amplifier, and the like, and perform modulation and poweramplification or the like on data output from the control unit 130, andtransmit the resultant data.

For example, the wireless communication unit 110 according to thisembodiment transmits a multicast frame. Thereafter, the wirelesscommunication unit 110 receives an ACK frame transmitted back from awireless terminal 200 which has succeeded in receiving the multicastframe. Note that, in addition to multicast communication, the wirelesscommunication unit 110 can transmit data using unicast communication orbroadband communication.

The wireless communication unit 110 may perform beamforming. Forexample, the wireless communication unit 110 may transmit a unicastframe, or perform beamforming to transmit a unicast frame, to any one ofthe wireless terminals 200. Similarly, the wireless communication unit110 may transmit a multicast frame, or perform beamforming to transmit amulticast frame, to any one or more of the wireless terminals 200.Beamforming is a technique of performing transmission with directivityin a particular direction so that the possibility that a wirelessterminal in the particular direction will succeed in receiving awireless signal can be improved. Typically, beamforming can be performedwith respect to a wireless terminal having a high channel correlation.

The wireless communication unit 110 may perform beamforming during frameretransmission. In this case, not only the possibility that a wirelessterminal 200 requiring retransmission will succeed in receiving a frameincreases, but also the possibility that another wireless terminal 200will succeed in receiving the frame and transmit an ACK frame backdecreases. For example, in the example shown in FIG. 1, it is assumedthat an ACK frame corresponding to multicast transmission from the basestation 100 is not transmitted back from the wireless terminals 200E and200F. In this case, if the base station 100 performs beamforming whichimparts directivity in the directions of the wireless terminal 200E and200F, the possibility that the wireless terminal 200E and 200F willsucceed in receiving a retransmitted frame can be increased. Meanwhile,if the wireless terminals 200A to 200D succeed in receiving aretransmitted frame, the wireless terminals 200A to 200D will transmitan ACK frame again. If the base station 100 performs beamforming whichimparts directivity in the directions of the wireless terminals 200E and200F, the probability that the wireless terminals 200A to 200D will failto receive a retransmitted frame can be increased. Thus, by performingbeamforming during frame retransmission, the base station 100 candecrease the possibility that an unnecessary ACK frame will betransmitted, and thereby increase the system throughput.

For example, when there are a plurality of wireless terminals 200 towhich retransmission is to be performed, the wireless communication unit110 may perform beamforming on a multicast frame. Alternatively, whenthere is a single wireless terminal 200 to which retransmission is to beperformed, the wireless communication unit 110 may perform beamformingon a unicast frame. When there is a single wireless terminal to whichretransmission is to be performed, then if the wireless communicationunit 110 uses a unicast frame, a wireless terminal 200 to whichretransmission is not to be performed can avoid transmitting an ACKframe.

(2) Storage Unit 120

The storage unit 120 is a part which records and retrieves data to andfrom a predetermined recording medium. The storage unit 120 isimplemented as, for example, a hard disc drive (HDD). Needless to say,the recording medium may be various recording media, such as asolid-state memory, such as a flash memory or the like, a memory cardincluding a solid-state memory, an optical disc, a magneto-optical disc,a hologram memory, and the like. The storage unit 120 may be configuredto be capable of recording and retrieval suitable for a recording mediumwhich is employed.

For example, according to this embodiment, the storage unit 120 storesidentification information of a wireless terminal 200 which hastransmitted back an ACK frame corresponding to multicast transmission.As a result, the base station 100 can manage information of a wirelessterminal 200 which has transmitted an ACK frame back, and therefore,avoid unnecessary retransmission. Also, the storage unit 120 may storedefault transmission settings. The transmission settings stored in thestorage unit 120 may include, for example, a frequency channel which isused, timings, the number of times of retransmission, and the like.

(3) Control Unit 130

The control unit 130 functions as a computation device and a controldevice to control general operations in the base station 100 accordingto various programs. The control unit 130 is implemented by anelectronic circuit such as, for example, a central processing unit(CPU), microprocessor, or the like. Note that the control unit 130 mayinclude a read only memory (ROM) for storing a program, computationparameters, and the like which are used, and a random access memory fortemporarily storing parameters or the like which are changed asappropriate. As shown in FIG. 2, the control unit 130 functions as acommunication control unit 131, a setting unit 133, a retransmissionmethod determination unit 135, and a retransmission timing determinationunit 137.

(3-1) Communication Control Unit 131

The communication control unit 131 has the function of controllingtransmission and reception processes which are performed by the wirelesscommunication unit 110. For example, the communication control unit 131controls multicast transmission which is performed by the wirelesscommunication unit 110. Also, the communication control unit 131controls a retransmission process which is performed by the wirelesscommunication unit 110.

The communication control unit 131 performs threshold determination onan index related to an ACK frame corresponding to multicasttransmission, to determine whether or not it is necessary to perform aframe retransmission process. This threshold is set by the setting unit133 described below. Various indexes related to an ACK framecorresponding to multicast transmission are conceived of.

For example, the index related to an ACK frame corresponding tomulticast transmission may be the number of wireless terminals 200 whichhave transmitted back an ACK frame corresponding to multicasttransmission. In this case, if the number of wireless terminals 200which have succeeded in reception and have transmitted an ACK frame hasnot reached the set threshold, the communication control unit 131determines that a frame which has been multicast-transmitted is to beretransmitted. Also, if the number of wireless terminals 200 which havesucceeded in reception and have transmitted an ACK frame has reached theset threshold, the communication control unit 131 determines that aframe which has been multicast-transmitted is not to be retransmitted.Note that the communication control unit 131 may perform thresholddetermination directly on the number of wireless terminals 200 whichhave transmitted back an ACK frame corresponding to multicasttransmission, or may perform threshold determination on a numericalvalue obtained by subjecting that number to processing such asincreasing or decreasing or the like.

Alternatively, for example, the index related to an ACK framecorresponding to multicast transmission may be the proportion ofwireless terminals 200 which has transmitted back an ACK framecorresponding to multicast transmission to wireless terminals 200 whichare a destination of multicast transmission. In this case, if the ratioof the number of wireless terminals 200 belonging to a multicast groupto the number of wireless terminals 200 which have succeeded inreception and are a transmission source of an ACK frame, has not reacheda threshold which is set, the communication control unit 131 determinesthat a frame which has been multicast-transmitted is to beretransmitted. Also, if the ratio of the number of wireless terminals200 belonging to a multicast group to the number of wireless terminals200 which have succeeded in reception and are a transmission source ofan ACK frame, has reached the threshold which is set, the communicationcontrol unit 131 determines that a frame which has beenmulticast-transmitted is not to be retransmitted. Note that thecommunication control unit 131 may perform threshold determinationdirectly on the proportion of wireless terminals 200 which havetransmitted back an ACK frame corresponding to multicast transmission towireless terminals 200 which are a destination of multicasttransmission, or may perform threshold determination on the proportionsubjected to processing such as increasing or decreasing or the like.

(3-2) Setting Unit 133

The setting unit 133 has the function of setting a threshold fordetermining whether or not it is necessary for the wirelesscommunication unit 110 to perform a retransmission process, on the basisof information about reception of an ACK frame corresponding tomulticast transmission from a wireless terminal 200.

As described above, the setting unit 133 sets a threshold related to theindex related to an ACK frame corresponding to multicast transmission.For example, the setting unit 133 may set a threshold related to thenumber of wireless terminals 200 which have transmitted back an ACKframe corresponding to multicast transmission. In this case, the settingunit 133 may set a threshold according to the number of wirelessterminals 200 to which multicast transmission is to be performed. Also,the setting unit 133 may set a threshold related to the proportion ofwireless terminals 200 which has transmitted back an ACK framecorresponding to multicast transmission to wireless terminals 200 whichare a destination of multicast transmission.

The setting unit 133 may set a threshold which is less than the totalnumber of wireless terminals 200 belonging to a multicast group. Forexample, when 10 wireless terminals 200 belong to a multicast group, thesetting unit 133 may set 5 terminals or a proportion of 0.5 as thethreshold. In this case, when 5 of the 10 wireless terminals havetransmitted an ACK frame back, the threshold is reached, and therefore,the communication control unit 131 assumes that multicast transmissionhas been successful, and does not perform retransmission. Thus, when thesetting unit 133 sets such a threshold that retransmission will not beperformed even when a portion of the wireless terminals 200 belonging toa multicast group have not transmitted an ACK frame back, whereby awaste of wireless resources can be avoided, and the system throughputcan be improved.

Various kinds of information about reception of an ACK frame, which area criterion on the basis of which the setting unit 133 sets thethreshold, are conceived of. For example, the information aboutreception of an ACK frame may be information indicating the level ofimportance of a multicast frame for which the reception of an ACK framehas resulted in failure. The setting unit 133 may calculate the aboveimportance level on the basis of information about a multicast frame forwhich the reception of an ACK frame has resulted in failure. An exampleof the importance level calculation will now be described.

(Calculation of Importance Level on Basis of Index of Upper Layer)

For example, the setting unit 133 calculates the importance level on thebasis of an index of an upper layer related to data contained in amulticast frame for which the reception of a corresponding ACK frame hasresulted in failure. Various indexes of an upper layer which are areference for calculation of the importance level are conceived of. Aspecific example of an index of an upper layer which is a reference forcalculation of the importance level will now be described.

Hierarchy of Encoding

For example, an index of an upper layer may be information indicatingthe encoding hierarchical level of data encoded by a hierarchicalencoding technique. During encoding, data may be generated at aplurality of different hierarchical levels. In this case, the settingunit 133 calculates the importance level according to a hierarchicallevel to which data containing a frame belongs. An example of thehierarchical encoding technique is a hierarchical encoding techniqueused in the Moving Picture Experts Group (MPEG). When a media stream isencoded using this encoding technique, data in the base layer and datain the enhancement layer are generated. The base layer is a data streamnecessary to decode a media stream. The enhancement layer is anaccompanying data stream for improving the quality of a stream in thebase layer. Wireless terminals 200 cannot decode a media stream when ithas failed to receive data in the base layer, and can decode a mediastream even when it has failed to receive data in the enhancement layer.This is because the enhancement layer is a layer which is provided inorder to improve the quality. Therefore, for example, the setting unit133 may calculate that the importance level is high for a framecontaining data in the base layer, and calculate that the importancelevel is low for a frame containing data in the enhancement layer.

Whether or not Video or Audio is Contained

For example, an index of an upper layer may be information indicatingwhether or not data contains at least any one of video and audio. Forexample, the setting unit 133 may calculate that the importance level ishigh for a frame containing video data or audio data, and calculate thatthe importance level is low for a frame containing neither video datanor audio data. Note that the value of the importance level may varydepending on the required system or application or the like. Forexample, in a moving image streaming service having high real-timeperformance, a case is conceived of where video data has a higherimportance level than that of audio data. Therefore, for example, thesetting unit 133 may calculate that the importance level is high for aframe containing video data, and calculate that the importance level islow for a frame containing audio data. Alternatively, for example, fordata which does not require real-time performance, such as contentdistribution from a server or the like, the setting unit 133 maycalculate that the importance level is high for a frame containing audiodata, and calculate that the importance level is low for a framecontaining video data.

Dependence Relationship with Other Data

For example, an index of an upper layer may be information indicating adependence relationship between data and other data contained in aframe. A dependence relationship may exist between pieces of data. Inthis case, the setting unit 133 may calculate the importance level ofdata contained in a frame according to the dependence relationshipbetween that data and other data. For example, for video data, there aretypes of data, i.e., I-pictures, P-pictures, and B-pictures. I-pictures,P-pictures, and B-pictures are used in a technique of compressing amoving image picture by predicting a current moving image picture frominformation of another moving image picture. I-pictures are a picturewhich is encoded without using prediction between pictures. An I-picturecontains information of a picture itself, and therefore, does not have adependence relationship with another picture. P-pictures are a picturewhich is encoded using only the previous picture as predictioninformation. A P-picture depends on an I-picture, because differenceinformation from the I-picture is encoded. B-pictures are a picturewhich is encoded using the previous and next pictures as predictioninformation. A B-picture depends on an I-picture, because differenceinformation from the I-picture is encoded. Thus, an I-picture isessential for decoding of a B-picture and a P-picture with reference tothe I-picture, and therefore, has a different importance level of datafrom those of the B-picture and the P-picture. Therefore, for example,the setting unit 133 may calculate that the importance level is high fora frame containing data of an I-picture, and calculate that theimportance level is low for a frame containing data of a P-picture or aB-picture.

Whether or not Protocol Header of Upper Layer is Contained

For example, an index of an upper layer may be information indicatingwhether or not data contained in a frame contains a protocol header ofan upper layer. The boundary between data frames, which are a unit ofwireless transmission, does not necessarily coincide with the boundarybetween packets of an upper-layer protocol (e.g., the TransmissionControl Protocol (TCP) or the User Datagram Protocol (UDP), etc.).Therefore, data frames which contain a header portion of an upper-layerprotocol and data frames which do not contain it may coexist. A headerportion of a protocol contains important information for correctlydeciphering data. Therefore, if a wireless terminal 200 has failed toreceive a header portion of a protocol, then even when the reception ofthe other portion corresponding to data has resulted in success, it isdifficult to correctly decipher the data. Therefore, for example, thesetting unit 133 may calculate that the importance level is high for aframe containing a protocol header of an upper layer such as TCP, UDP,or the like, and calculate that the importance level is low for theother frames.

Whether or not Time Stamp is Contained

For example, an index of an upper layer may be information indicatingwhether or not data contains a time stamp. For example, it is conceivedthat the base station 100, when transmitting video data or audio data,uses the MPEG system layer. A MPEG time stamp contained in the MPEGlayer is used to synchronize different contents, such as audio, video,and the like, with each other. Therefore, when a wireless terminal 200has failed to receive an MPEG time stamp, a situation may occur in whichcontents which are desired to be output simultaneously as the behaviorof an application are output at different timings. For example, asituation may occur in which timings of a moving image at which an actoror actress in a film is speaking, may not be synchronous with timings atwhich lines which are spoken are heard. In addition, when a wirelessterminal 200 has failed to receive an MPEG time stamp, a situation mayoccur in which video or audio is not smoothly played back. In such asituation, the occurrence of reception error is likely to be clearlynoticed by the user. Therefore, it is desirable that such a situationshould be avoided. Therefore, for example, the setting unit 133 maycalculate that the importance level is high for a frame which contains atime stamp, and calculate that the importance level is low for a framewhich does not contain a time stamp.

In the foregoing, an example of the importance level calculation basedon an index of an upper layer has been described. Note that the settingunit 133 may acquire various indexes of upper layers from thecorresponding upper layers using, for example, an interface called“primitive.”

The setting unit 133 sets the threshold on the basis of the calculatedimportance level. For example, the setting unit 133 may set a highthreshold for a frame having a high importance level. In this case, fora frame having a high importance level, the communication control unit131 repeatedly performs retransmission until many wireless terminals 200have transmitted an ACK frame back. Meanwhile, the setting unit 133 mayset a low threshold for a frame having a low importance level. In thiscase, for a frame having a low importance level, the communicationcontrol unit 131 will not perform retransmission, even when only a fewwireless terminals 200 have transmitted an ACK frame back. As a result,the communication control unit 131 can perform the retransmissionprocess according to the importance level of a frame, i.e., can givepriority to reliable reception for a frame having a high importancelevel, and can give priority to improvement of the system throughput fora frame having a low importance level.

(Supplements)

The setting unit 133 may calculate the importance level by combining aplurality of indexes of an upper layer. Also, the setting unit 133 mayset two or more importance levels. Also, the importance level may have acontinuous value or a discrete value.

Also, as the information about reception of an ACK frame correspondingto multicast transmission from a wireless terminal 200, the setting unit133 may set the threshold on the basis of the number of wirelessterminals 200 belonging to a multicast group. For example, the settingunit 133 may set a higher threshold as the number of wireless terminals200 belonging to a multicast group increases, and may set a lowerthreshold as the number of wireless terminals 200 belonging to amulticast group decreases.

Also, the setting unit 133 may dynamically calculate and set athreshold, or may set a fixed value stored in the storage unit 120. Ineither case, if the setting unit 133 sets such a threshold that theretransmission process will not be performed even when a portion of thewireless terminals 200 belonging to a multicast group have nottransmitted an ACK frame back, a waste of wireless resources can beavoided.

(3-3) Retransmission Method Determination Unit 135

The retransmission method determination unit 135 has the function ofdetermining a method of transmitting a retransmission frame in theretransmission process performed by the communication control unit 131.For example, the retransmission method determination unit 135 determinesa transmission method on the basis of information about a wirelessterminal 200 which has failed to receive an ACK frame corresponding tomulticast transmission. Various transmission methods in theretransmission process are conceived of. A specific example of atransmission method in the retransmission process will now be described.

Beamforming

For example, the retransmission method determination unit 135 maydetermine whether or not beamforming is to be performed. For example,the retransmission method determination unit 135 may determine thatbeamforming is to be performed if wireless terminals 200 to whichretransmission is to be performed include one that has a high channelcorrelation, and may determine that transmission without directivity isto be performed if none of the wireless terminals 200 has a high channelcorrelation. Alternatively, the retransmission method determination unit135 may determine that beamforming is to be performed if the number ofwireless terminals 200 which have a high channel correlation, ofwireless terminal 200 to which retransmission is to be performed, issufficient to satisfy the threshold, and otherwise, may determine thattransmission without directivity is to be performed.

Multicast Transmission/Unicast Transmission

For example, the retransmission method determination unit 135 maydetermine whether multicast transmission is to be performed or unicasttransmission is to be performed. For example, the retransmission methoddetermination unit 135 may determine that unicast transmission is to beperformed if the number of wireless terminals 200 which are required sothat the threshold is satisfied is one, and may determine that multicasttransmission is to be performed if the number of wireless terminals 200which are necessary to satisfy the threshold is plural.

Thus, the retransmission method determination unit 135 can determine anefficient transmission method for satisfying the threshold, on the basisof information about a wireless terminal 200 which has failed to receivean ACK frame corresponding to multicast transmission. As a result, theretransmission process is more efficiently performed, resulting in animprovement in the system throughput.

(3-4) Retransmission Timing Determination Unit 137

The retransmission timing determination unit 137 has the function ofdetermining a timing at which the communication control unit 131performs the retransmission process. For example, it is assumed that adefault retransmission timing is a timing immediately after all framesthat had already been scheduled to be transmitted when it was determinedthat retransmission is to be performed have been transmitted. Theretransmission timing determination unit 137, when retransmitting aframe, changes the default retransmission timing by setting a waitingtime until retransmission, depending on a situation.

For example, there may be interference from another system employing thesame frequency band, such as radio wave interference from a microwaveoven in the 2.4-GHz band of wireless LAN. Therefore, the retransmissiontiming determination unit 137 may check conditions of a frequencychannel used for transmission, and when there is interference, may set awaiting time so that the retransmission timing is later than thedefault. At this time, the retransmission timing determination unit 137may determine whether or not the retransmission timing is to be changed,or may adjust the length of the waiting time, depending on the strengthof the interference. As a result, the wireless terminals 200 can beprevented from failing to receive a retransmission frame due tointerference, resulting in a reduction in unnecessary retransmission.

Here, another process such as, for example, transmission of anotherframe or the like, may be performed during the waiting time until theretransmission timing. Note that, for successive frames, theretransmission timing determination unit 137 may stop transmission offrames following a frame to be retransmitted. Specifically, theretransmission timing determination unit 137 may determine that aretransmission process is to be performed before a frame that follows.As a result, a receiver can receive successive frames in that order, sothat a reordering process will not be performed, and therefore, theprocess load can be reduced. Note that if a following frame had alreadybeen transmitted when it was determined that retransmission is to beperformed, the retransmission timing determination unit 137 determinesthat a retransmission process is to be performed before a frame laterthan that frame.

Thus, the retransmission timing determination unit 137 can determine anappropriate retransmission timing. As a result, useless retransmissioncan be reduced, or the process load on the receiver can be reduced.

In the foregoing, a configuration example of the base station 100according to this embodiment has been described. Next, an operationprocess example of the base station 100 according to this embodimentwill be described with reference to FIG. 3 to FIG. 6.

[2-3. Operation Process Examples] (Retransmission Process)

FIG. 3 is a flowchart showing a flow example of a retransmission processperformed in the base station 100 according to this embodiment.

As shown in FIG. 3, initially, in step S102, the setting unit 133performs a threshold setting process. This process will not now bedescribed, because it will be described below with reference to FIG. 4.

Next, in step S104, the wireless communication unit 110 transmits amulticast frame.

Next, in step S106, the wireless communication unit 110 receives an ACKframe which is transmitted back from a wireless terminal 200 which hassucceeded in receiving the multicast frame transmitted in step S104. Atthis time, the communication control unit 131 reads identificationinformation of the wireless terminal 200, which is a transmissionsource, from the ACK frame received from the wireless terminal 200, andstores the identification information, as a terminal which has succeededin receiving a multicast frame, in the storage unit 120. Thecommunication control unit 131 performs a similar process each timeretransmission is subsequently performed, and manages terminals of amulticast group which have succeeded in reception, and the otherterminals which have failed. As the identification information of awireless terminal 200, a MAC address may be used, for example.

Next, in step S108, the communication control unit 131 performs athreshold determination process. Specifically, the communication controlunit 131 determines whether or not an index related to an ACK frame thereception of which has resulted in success in step S106 has reached thethreshold set in step S102. For example, when the threshold is thenumber of terminals which have transmitted an ACK frame back, thecommunication control unit 131 determines whether or not the number ofwireless terminals 200 which have transmitted back an ACK framecorresponding to multicast transmission is greater than or equal to thethreshold. Also, when the threshold is the proportion of terminals whichhave transmitted an ACK frame back, the communication control unit 131determines whether or not the proportion of wireless terminals 200 whichhave transmitted back the ACK frame corresponding to multicasttransmission to the wireless terminals 200 which are a destination ofmulticast transmission is greater than or equal to the threshold.

If the threshold has not been reached (S110/YES), in step S112 theretransmission method determination unit 135 performs a retransmissionmethod determination process. This process will not now be described,because it will be described below with reference to FIG. 5.

Next, in step S114, the retransmission timing determination unit 137performs a retransmission timing determination process. This processwill not now be described, because it will be described below withreference to FIG. 6.

Thereafter, in step S116, the wireless communication unit 110retransmits the frame. Here, the wireless communication unit 110 mayperform multicast transmission, may perform unicast transmission, mayperform beamforming, or may perform transmission without directivity,depending on the process result in step S112. Also, the wirelesscommunication unit 110 retransmits the frame at the retransmissiontiming indicated by the process result in step S114.

Thereafter, the process returns to step S106 again.

Meanwhile, if the result of the threshold determination process in stepS108 is greater than or equal to the threshold (S110/NO), the process isended. Thereafter, for example, step S102 and following steps arerepeatedly performed for frames following the frame transmitted in stepS104.

In the foregoing, a flow example of the retransmission process accordingto this embodiment has been described. Next, the threshold settingprocess, the retransmission method determination process, and theretransmission timing determination process in the above retransmissionprocess will be described with reference to FIG. 4 to FIG. 6.

(Threshold Setting Process)

FIG. 4 is a flowchart showing a flow example of the threshold settingprocess performed in the base station 100 according to this embodiment.This process corresponds to the process in step S102 of FIG. 3.

As shown in FIG. 4, initially, in step S202, the setting unit 133acquires an index of an upper layer related to a frame. For example, thesetting unit 133 acquires information indicating the hierarchy ofencoding, whether or not video or audio is contained, the dependencerelationship with other data, whether or not a protocol header of anupper layer is contained, whether or not a time stamp is contained, andthe like. Note that the frame as used here refers to a multicast framewhich is transmitted by the base station 100 in step S104 of FIG. 3. Thesame applies to the description that follows.

Next, in step S204, the setting unit 133 calculates the importance levelof the frame on the basis of the index of the upper layer acquired instep S202. For example, the setting unit 133 calculates the importancelevel of the frame, taking into consideration all of the importancelevels calculated on the plurality of indexes of an upper layer whichhave been acquired.

Thereafter, in step S206, the setting unit 133 sets the thresholdaccording to the importance level calculated in step S204. For example,the setting unit 133 sets a higher threshold as the importance levelincreases, and a lower threshold as the importance level decreases. Notethat the threshold as used here may be set as, for example, the numberof terminals which have transmitted an ACK frame back, or may be set asthe proportion of terminals which have transmitted an ACK frame back.

In the foregoing, a flow example of the threshold setting processaccording to this embodiment has been described.

(Retransmission Method Determination Process)

FIG. 5 is a flowchart showing a flow example of the retransmissionmethod determination process performed in the base station 100 accordingto this embodiment. This process corresponds to the process in step S112of FIG. 3.

As shown in FIG. 5, initially, in step S302, the retransmission methoddetermination unit 135 determines whether or not there are a pluralityof wireless terminals 200 which are retransmission destinationsnecessary to satisfy the threshold. For example, the number of wirelessterminals 200 necessary to satisfy the threshold is represented by a. Inthis case, if a wireless terminals 200 have transmitted an ACK frameback after retransmission of the frame, the threshold is satisfied.

If α>1 (S302/YES), in step S304 the retransmission method determinationunit 135 determines whether or not there is a set of retransmissioncandidates having a high channel correlation. Specifically, theretransmission method determination unit 135 determines whether or notthere is a set of wireless terminals 200 having a high channelcorrelation, of wireless terminals 200 which have not transmitted an ACKframe back.

If there is not a set of retransmissions having a high channelcorrelation (S304/NO), in step S314 the retransmission methoddetermination unit 135 determines that multicast transmission is to beperformed without directivity (without beamforming).

Meanwhile, if there is a set of retransmissions having a high channelcorrelation (S304/YES), in step S306 the retransmission methoddetermination unit 135 determines whether or not there is a setexceeding the threshold. Specifically, the retransmission methoddetermination unit 135 determines whether or not there is a set of a ormore wireless terminals 200, of the sets of wireless terminals 200 whichhave not transmitted an ACK frame back and have a high channelcorrelation.

If it is determined that there is not a set exceeding the threshold(S306/NO), in step S314 the retransmission method determination unit 135determines that multicast transmission is to be performed withoutdirectivity.

If it is determined that there is a set exceeding the threshold(S306/YES), in step S308 the retransmission method determination unit135 determines whether or not there are a plurality of sets exceedingthe threshold.

If it is determined that there are a plurality of sets exceeding thethreshold (S308/YES), in S310 the retransmission method determinationunit 135 selects a set including the largest number of wirelessterminals 200, of the sets exceeding the threshold. This selectioncriterion is merely an example, and the present technology is notlimited to this example. For example, the retransmission methoddetermination unit 135 may select a set including the smallest number ofwireless terminals 200, or may select a set having the highest channelcorrelation, or may select a set allowing transmission at the highestthroughput. Thereafter, in step S312, the retransmission methoddetermination unit 135 determines that beamforming is to be performedand multicast transmission is to be performed. At this time, theretransmission method determination unit 135 determines that beamformingis to be performed with respect to the set selected in step S310.

Meanwhile, if it is determined that there is a single set exceeding thethreshold (S308/NO), in step S312 the retransmission methoddetermination unit 135 determines that beamforming is to be performedwith respect to the set, and multicast transmission is to be performed.

Meanwhile, if it is determined in step S302 that there is a singlewireless terminal 200 which is a retransmission destination necessary tosatisfy the threshold, i.e., it is determined that α=1 (S302/NO), theprocess proceeds to step S316. In step S316, the retransmission methoddetermination unit 135 determines whether or not there are a pluralityof retransmission candidates. Specifically, the retransmission methoddetermination unit 135 determines whether or not there are a pluralityof wireless terminals 200 which have not transmitted an ACK frame back.

If it is determined that there are a plurality of retransmissioncandidates (S316/YES), in step S318 the retransmission methoddetermination unit 135 selects a wireless terminal 200 having thehighest throughput, of the retransmission candidates. Note that thisselection criterion is merely an example, and the present technology isnot limited to this. For example, the retransmission methoddetermination unit 135 may randomly select a single wireless terminal200. Thereafter, in step S320, the retransmission method determinationunit 135 determines that beamforming is to be performed and unicasttransmission is to be performed with respect to the selected wirelessterminal 200.

Meanwhile, if it is determined that there is a single retransmissioncandidate (S316/NO), in step S320 the retransmission methoddetermination unit 135 determines that beamforming is to be performedand unicast transmission is to be performed with respect to the wirelessterminal 200 which is a retransmission candidate.

According to the result of the above-described retransmission methoddetermination process, the wireless communication unit 110 performs theretransmission process. For example, when there are a plurality ofwireless terminals 200 which are retransmission destinations necessaryto satisfy the threshold, the wireless communication unit 110 performsmulticast transmission. Also, the wireless communication unit 110performs beamforming if there is a set of retransmission candidateshaving a high channel correlation, and performs transmission withoutbeamforming if there is not a set of retransmission candidates having ahigh channel correlation. Also, when there is a single wireless terminal200 which is a retransmission destination necessary to satisfy thethreshold, the wireless communication unit 110 performs beamforming andunicast transmission.

In the foregoing, a flow example of the retransmission methoddetermination process according to this embodiment has been described.

(Retransmission Timing Determination Process)

FIG. 6 is a flowchart showing a flow example of the retransmissiontiming determination process performed in the base station 100 accordingto this embodiment. This process corresponds to the process in step S114of FIG. 3.

As shown in FIG. 6, initially, in step S402, the retransmission timingdetermination unit 137 determines whether or not there is interference.For example, the retransmission timing determination unit 137 checksconditions of a frequency channel used for transmission, to determinewhether or not there is interference from another system employing thesame similar frequency band, such as radio wave interference from amicrowave oven in the 2.4-GHz band of wireless LAN.

If it is determined that there is interference (S402/YES), in step S404the retransmission timing determination unit 137 determines that aretransmission process is to be performed after waiting for apredetermined period of time. Note that the retransmission timingdetermination unit 137 may adjust the length of the waiting time untilretransmission is performed, depending on the strength of theinterference.

Meanwhile, if it is determined that there is not interference (S402/NO),in step S406 the retransmission timing determination unit 137 determineswhether or not the retransmission is the first retransmission. Forexample, when a frame is to be retransmitted for the first time, theretransmission timing determination unit 137 determines that theretransmission is the first retransmission. When a frame which hasalready been retransmitted is to be retransmitted again, theretransmission timing determination unit 137 determines that theretransmission is the second retransmission or following.

If it is determined that the retransmission is the first retransmission(S406/YES), in step S408 the retransmission timing determination unit137 determines that a retransmission process is to be performed beforethe following frame. As a result, it is possible that the receiver willnot perform the process of reordering, and the process load can bereduced.

Meanwhile, if it is determined that the retransmission is the secondretransmission or following (S406/NO), in step S410 the retransmissiontiming determination unit 137 determines that a retransmission processis to be performed at a default timing. For example, the retransmissiontiming determination unit 137 determines that a frame to beretransmitted is to be transmitted after all frames scheduled to betransmitted have already been transmitted.

In the foregoing, a flow example of the retransmission timingdetermination process according to this embodiment has been described.

[2-4. Variation 1]

This variation is an embodiment in which the threshold is set on thebasis of a transmission setting. A base station 100 according to thisvariation has a configuration similar to that which has been describedabove with reference to FIG. 2. A characteristic configuration of thisvariation will now be described.

(Calculation of Importance Level on Basis of Transmission Setting)

A setting unit 133 according to this variation calculates the importancelevel on the basis of a transmission setting which has been used duringtransmission of a multicast frame. Various transmission settings whichare criteria for calculation of the importance level are conceived ofSpecific examples of a transmission setting which is a criterion forcalculation of the importance level, will now be described.

Settings for Transmission in Bundle of Plurality of Frequency Channels

For example, a transmission setting which is a criterion for calculationof the importance level may be a setting for transmission in a bundle ofa plurality of frequency channels. This setting is also called, forexample, channel bonding. In the base station 100, the throughput can beimproved by using channel bonding. For example, the setting unit 133 maycalculate that the importance level is high for a frame transmittedusing channel bonding, and calculate that the importance level is lowfor a frame transmitted without using channel bonding.

Frequency Channel

For example, a transmission setting which is a criterion for calculationof the importance level may be a setting for a frequency channel. Thethroughput may vary from frequency channel to frequency channel. In thiscase, for example, the base station 100 may transmit more important datausing a frequency channel having a higher throughput. Therefore, forexample, the setting unit 133 may calculate that the importance level ishigh for a frame transmitted using a frequency channel having a highthroughput, and calculate that the importance level is low for a frametransmitted using a frequency channel having a low throughput.

In the foregoing, an example of calculation of the importance level onthe basis of a transmission setting, has been described. Note that thesetting unit 133 may calculate the importance level using a combinationof a plurality of transmission settings, or calculate the importancelevel additionally using the plurality of indexes of an upper layeraccording to the first embodiment. The setting unit 133 sets thethreshold on the basis of the calculated importance level of a multicast frame.

In the foregoing, a characteristic configuration of the setting unit 133according to this variation has been described. Next, an operationprocess example of the base station 100 according to this variation willbe described. An operation process of the base station 100 according tothis variation is similar to that of the first embodiment, except forthe threshold setting process. Therefore, a threshold setting processaccording to this variation will be described with reference to FIG. 7.

(Threshold Setting Process)

FIG. 7 is a flowchart showing a flow example of the threshold settingprocess performed in the base station 100 according to this variation.This process corresponds to the process in step S102 of FIG. 3.

As shown in FIG. 7, initially, in step S502, the setting unit 133acquires information indicating a transmission setting for a frame. Forexample, the setting unit 133 acquires information indicating a settingfor channel bonding and a setting for a frequency channel. Note that theframe as used here refers to a multicast frame which is transmitted bythe base station 100 in step S104 of FIG. 3. The same applies to thedescription that follows.

Next, in step S504, the setting unit 133 calculates the importance levelof the frame on the basis of the information indicating the transmissionsettings which have been acquired in step S502. For example, the settingunit 133 calculates the importance level of the frame, taking intoconsideration all of the importance levels calculated on the informationindicating the transmission settings which have been acquired.

Thereafter, in step S506, the setting unit 133 sets the thresholdaccording to the importance level calculated in step S504. For example,the setting unit 133 sets a higher threshold as the importance levelincreases, and sets a lower threshold as the importance level decreases.Note that, here, for example, the threshold may be set as the number ofterminals which have transmitted an ACK frame back, or may be set as theproportion of terminals which have transmitted an ACK frame back.

In the foregoing, a flow example of the threshold setting processaccording to this variation has been described.

[2-5. Variation 2]

This variation is an embodiment in which the threshold is set on thebasis of information about an MAC layer. The base station 100 accordingto this variation has a configuration similar to that which has beendescribed above with reference to FIG. 2. A characteristic configurationof this variation will now be described.

(Calculation of Importance Level on Basis of Information about MACLayer)

A setting unit 133 according to this variation calculates the importancelevel on the basis of information about a media access control (MAC)layer of a multicast frame. Various kinds of information about an MAClayer which is a criterion for calculation of the importance level areconceived of. A specific example of information about an MAC layer whichis a criterion for calculation of the importance level will now bedescribed.

Type of Multicast Frame

For example, the information about an MAC layer which is a criterion forcalculation of the importance level may be the type of a multicastframe. For example, the setting unit 133 may calculate the importancelevel on the basis of the type of a frame based on an access categorycompliant with the IEEE802.11 standard. In IEEE802.11, data frames aredivided into four categories (AC_VO, AC_VI, AC_BE, and AC_BK) so thatthe transmission opportunity, continuous transmission allowable time,and the like of data are differentiated according to quality required byan application. For example, the priority of AC_VO may be ranked first,the priority of AC_VI may be ranked second, the priority of AC_BE may beranked third, and the priority of AC_BK may be ranked fourth. Therefore,for example, the setting unit 133 may calculate that the importancelevel is highest for a frame of AC_VO, calculate that the importancelevel is second highest for AC_VI, calculate that the importance levelis third highest for AC_BE, and calculate that the importance level isfourth highest for AC_BK.

Data Amount of Multicast Frame

For example, the information about an MAC layer which is a criterion forcalculation of the importance level may be information indicating thedata amount of a multicast frame. For example, the setting unit 133 maycalculate that the importance level is higher as the data amount of aframe increases, and calculate that the importance level is lower as thedata amount decreases.

In the foregoing, an example of calculation of the importance level onthe basis of the information about an MAC layer has been described. Notethat the setting unit 133 may calculate the importance level using acombination of information about a plurality of MAC layers, or calculatethe importance level additionally using a combination of a plurality ofindexes of an upper layer according to the first embodiment and/or atransmission setting according to Variation 1. The setting unit 133 setsthe threshold on the basis of the calculated importance level of amulticast frame.

In the foregoing, a characteristic configuration of the setting unit 133according to this variation has been described. Next, an operationprocess example of the base station 100 according to this variation willbe described. The operation process of the base station 100 according tothis variation is similar to that of the first embodiment, except forthe threshold setting process. Therefore, a threshold setting processaccording to this variation will be described with reference to FIG. 8.

(Threshold Setting Process)

FIG. 8 is a flowchart showing a flow example of the threshold settingprocess performed by the base station 100 according to this variation.This process corresponds to the process in step S102 of FIG. 3.

As shown in FIG. 8, initially, in step S602, the setting unit 133acquires information about an MAC layer. For example, the setting unit133 acquires information indicating the type of a frame and the dataamount of the frame. Note that the frame as used here refers to amulticast frame which is transmitted by the base station 100 in stepS104 of FIG. 3. The same applies to the description that follows.

Next, in step S604, the setting unit 133 calculates the importance levelof the frame on the basis of the information about an MAC layer acquiredin step S602. For example, the setting unit 133 calculates theimportance level of the frame, taking into consideration each importancelevel calculated on the basis of the acquired information about an MAClayer.

Thereafter, in step S606, the setting unit 133 sets the thresholdaccording to the importance level calculated in step S604. For example,the setting unit 133 set a higher threshold as the importance levelincreases, and sets a lower threshold as the importance level decreases.Note that, here, for example, the threshold may be set as the number ofterminals which have transmitted an ACK frame back, or may be set as theproportion of terminals which have transmitted an ACK frame back.

In the foregoing, a flow example of the threshold setting processaccording to this variation has been described.

3. Second Embodiment

This embodiment is one in which by performing threshold determination onthe number of times of retransmission of a frame, it is determinedwhether or not retransmission is to be performed. A base station 100according to this embodiment has a configuration similar to that whichhas been described above with reference to FIG. 2. A characteristicconfiguration of this embodiment will now be described.

[3-1. Configuration Examples of Base Station] (Communication ControlUnit 131)

The communication control unit 131 according to this embodimentdetermines whether or not it is necessary to perform a frameretransmission process by performing threshold determination on an indexabout the number of times of retransmission of a frame which has beenmulticast-transmitted. This threshold (the maximum number of times ofretransmission) is set by the setting unit 133. For example, if thenumber of times of retransmission of a frame has not reached the setthreshold, the communication control unit 131 determines that the frameis to be retransmitted. Also, if the number of times of retransmissionof a frame has reached the set threshold, the communication control unit131 determines that the frame is not to be retransmitted. Note that thecommunication control unit 131 may perform threshold determinationdirectly on the number of times of retransmission, or perform thresholddetermination on a numerical value obtained by subjecting that number toprocessing such as increasing or decreasing or the like.

(Setting Unit 133)

The setting unit 133 has the function of setting a threshold for thenumber of times of retransmission which is for determining whether ornot it is necessary for the wireless communication unit 110 to perform aretransmission process. For example, the setting unit 133 may calculatethe importance level of a multicast frame using the criterion describedabove in the first embodiment, and set the maximum number of times ofretransmission according to the calculated importance level. Forexample, the setting unit 133 may set a high maximum number of times ofretransmission for a frame having a high importance level. In this case,the communication control unit 131 can retransmit a frame having a highimportance level a larger number of times. Meanwhile, the setting unit133 may set a low maximum number of times of retransmission for a framehaving a low importance level. In this case, the communication controlunit 131 can end retransmission after a smaller number of times for aframe having a low importance level. As a result, the communicationcontrol unit 131 can perform a retransmission process according to theimportance level of a frame, i.e., can give priority to reliablereception for a frame having a high importance level, and can givepriority to improvement of the system throughput for a frame having alow importance level.

In the foregoing, a characteristic configuration of the base station 100according to this embodiment has been described. Next, an operationprocess example of the base station 100 according to this embodimentwill be described with reference to FIG. 9.

[3-2. Operation Process Example]

FIG. 9 is a flowchart showing a flow example of a retransmission processperformed in the base station 100 according to this embodiment.

As shown in FIG. 9, initially, in step S702, the setting unit 133performs a process of setting the maximum number of times ofretransmission. For example, the setting unit 133 calculates theimportance level of a frame by a process similar to that in the firstembodiment, and sets the maximum number of times of retransmissionaccording to the calculated importance level.

Next, in step S704, the wireless communication unit 110 transmits amulticast frame.

Next, in step S706, the wireless communication unit 110 receives an ACKframe which is transmitted back from a wireless terminal 200 which hassucceeded in receiving the multicast frame transmitted in step S104. Atthis time, the communication control unit 131 reads identificationinformation of the wireless terminal 200 which is the transmissionsource, from the ACK frame received from the wireless terminal 200, andstores the identification information, as a terminal from which thereception of the multicast frame has resulted in success, in the storageunit 120. The communication control unit 131 performs a similar processeach time retransmission is subsequently performed, and managesterminals of a multicast group which have succeeded in reception, andthe other terminals which have failed. As the identification informationof a wireless terminal 200, a MAC address may be used, for example.

Next, in step S708, the communication control unit 131 determineswhether or not there is any wireless terminal 200 that has nottransmitted an ACK frame back. Specifically, the communication controlunit 131 determines whether or not there is any wireless terminal 200that has not transmitted an ACK frame back, of the wireless terminals200 belonging to a multicast group.

If there is a wireless terminal 200 which has not transmitted an ACKframe back (S708/YES), in step S710 the communication control unit 131performs a process of determining the number of times of retransmission.Specifically, the communication control unit 131 determines whether ornot the number of times of retransmission performed in step S718described below has reached the maximum number of times ofretransmission set in step S702.

If the number of times of retransmission is less than the maximum numberof times of retransmission (S712/YES), in step S714 the retransmissionmethod determination unit 135 performs a retransmission methoddetermination process. This process is as described above with referenceto FIG. 5.

Next, in step S716, the retransmission timing determination unit 137performs a retransmission timing determination process. This process isas described above with reference to FIG. 6.

Thereafter, in step S718, the wireless communication unit 110retransmits the frame. Here, the wireless communication unit 110 mayperform multicast transmission, perform unicast transmission, performbeamforming, or perform transmission without directivity, depending onthe process result in step S714. Also, the wireless communication unit110 retransmits the frame at a retransmission timing indicated by theprocess result in step S716.

Thereafter, the process returns to step S706 again.

Meanwhile, if it is determined in step S708 that there is not a wirelessterminal 200 which has not transmitted an ACK frame back (S708/NO), orif the number of times of retransmission has reached the maximum numberof times of retransmission (S712/NO), the process is ended. Thereafter,for example, for frames following the frame transmitted in step S704,step S702 and following steps are repeated performed.

In the foregoing, a flow example of the retransmission process accordingto this embodiment has been described.

4. Application Examples

The technology according to the present disclosure is applicable tovarious products. For example, the wireless terminal 200 may beimplemented as a mobile terminal, such as a smartphone, tablet personalcomputer (PC), notebook PC, hand-held game terminal, digital camera, orthe like, a stationary terminal, such as a television set, printer,digital scanner, network storage, or the like, or an on-vehicleterminal, such as a car navigation apparatus or the like. Also, thewireless terminal 200 may be implemented as a terminal for performingmachine-to-machine (M2M) communication (also referred to as a machinetype communication (MTC) terminal), such as a smart meter, vendingmachine, remote monitoring apparatus, point of sale (POS) terminal, orthe like. Furthermore, the wireless terminal 200 may be a wirelesscommunication module (e.g., an integrated circuit module configured on asingle die) mounted on these terminals.

Meanwhile, for example, the base station 100 may be implemented as awireless LAN access point (also referred to as a wireless base station)which has a router function or does not have a router function. Also,the base station 100 may be implemented as a mobile wireless LAN router.Furthermore, the base station 100 may be a wireless communication module(e.g., an integrated circuit module configured on a single die) which ismounted on these apparatuses.

FIG. 10 is a block diagram showing a schematic configuration example ofa wireless access point 950 to which the technology according to thepresent disclosure is applied. The wireless access point 950 includes acontroller 951, a memory 952, an input device 954, a display device 955,a network interface 957, a wireless communication interface 963, anantenna switch 964, and an antenna 965.

The controller 951 may be, for example, a CPU or a digital signalprocessor (DSP), and operates various functions (e.g., accessrestriction, routing, encryption, fire wall, log management, etc.) ofthe internet protocol (IP) layer and higher layers of the wirelessaccess point 950. The memory 952 includes a RAM and a ROM, and stores aprogram executed by the controller 951 and various kinds of control data(e.g., a terminal list, routing table, encryption key, security setting,log, etc.).

The input device 954 includes, for example, a button, switch, or thelike, and accepts the user's operation. The display device 955 includesan LED lamp or the like, and displays the status of an operation of thewireless access point 950.

The network interface 957 is a wired communication interface forallowing the wireless access point 950 to connect to a wiredcommunication network 958. The network interface 957 may include aplurality of connection terminals. The wired communication network 958may be a LAN, such as Ethernet (registered trademark) or the like, or awide area network (WAN).

The wireless communication interface 963 supports one or more ofwireless LAN standards, such as IEEE802.11a, 11b, 11g, 11n, 11AC, and11ad, and the like, and provides a wireless connection as an accesspoint to neighboring terminals. The wireless communication interface 963may typically include a baseband processor, RF circuit, power amplifier,and the like. The wireless communication interface 963 may be a one-chipmodule on which a memory for storing a communication control program, aprocessor for executing the program, and related circuits areintegrated. The antenna switch 964 switches a connection of the antenna965 between a plurality of circuits included in the wirelesscommunication interface 963. The antenna 965 has a single antennaelement or a plurality of antenna elements, and is used for transmissionand reception of a wireless signal by the wireless communicationinterface 963.

In the wireless access point 950 shown in FIG. 10, the wirelesscommunication unit 110, the storage unit 120, and the control unit 130,which have been described with reference to FIG. 2, may be implementedin the wireless communication interface 963. Also, at least a portion ofthese functions may be implemented in the controller 951. For example,if the wireless access point 950 functions as the base station 100, thewireless access point 950 can perform retransmission control in whichwireless resources are more efficiently utilized, on wireless terminalswithin the coverage of the wireless access point 950.

5. Conclusion

In the foregoing, the technology according to one embodiment of thepresent disclosure has been described in detail with reference to FIG. 1to FIG. 10. As described above, the base station 100 according to thisembodiment performs wireless communication, particularly multicasttransmission, with wireless terminals 200, and sets a threshold fordetermining whether or not it is necessary to perform a retransmissionprocess, depending on information about reception of an ACK framecorresponding to multicast transmission from wireless terminals 200. Bysetting the threshold, the base station 100 can be restrained fromperforming retransmission even when a portion of the wireless terminals200 belonging to a multicast group have not transmitted an ACK frameback. As a result, the base station 100 can perform retransmissioncontrol in which the number of times of retransmission, and the numberof times of transmission of an ACK frame accompanying retransmission,are reduced, whereby wireless resources can be more efficientlyutilized.

In the communication system 1 according to this embodiment, the droppingof a wireless data frame can be reduced, leading to an increase in datatransmission quality, compared to a communication system which does notuse an ACK frame. Furthermore, in the communication system 1 accordingto this embodiment, unnecessary retransmission or the number of ACKframes can be reduced, which contributes to a reduction in powerconsumption in the base station 100 and the wireless terminals 200, evencompared to a communication system which uses an ACK frame.

Also, the base station 100 has the retransmission method determinationunit 135 and the retransmission timing determination unit 137, and canretransmit a frame using a method and at a retransmission timing whichare suitable to contribute to an improvement in the system throughput.

Also, the setting unit 133 calculates the importance level of a frame,and sets the threshold on the basis of the importance level. As aresult, the base station 100 can adjust the amount of wireless resourceswhich are consumed in retransmission, depending on the importance level.For example, the setting unit 133 sets a high threshold for a framehaving a high importance level, and sets a low threshold for a framehaving a low importance level. In this case, the base station 100 cangive priority to reliable reception by allocating wireless resources fora frame having a high importance level, and can give priority toimprovement of the system throughput by limiting consumption of wirelessresources for a frame having a low importance level.

The preferred embodiment(s) of the present disclosure has/have beendescribed above with reference to the accompanying drawings, whilst thepresent disclosure is not limited to the above examples. A personskilled in the art may find various alterations and modifications withinthe scope of the appended claims, and it should be understood that theywill naturally come under the technical scope of the present disclosure.

For example, in the foregoing, it has been described that the settingunit 133 sets a high threshold for a frame having a high importancelevel, and sets a low threshold for a frame having a low importancelevel. The present technology is not limited to this example. Forexample, the setting unit 133 may set a low threshold for a frame havinga high importance level, and sets a high threshold for a frame having alow importance level. Alternatively, the setting unit 133 may set ahigher threshold as the importance level is closer to a predeterminedvalue, and set a lower threshold as the importance level is further awayfrom the predetermined value.

Also, the method of calculating the importance level by the setting unit133 has been described using a specific example. The present technologyis not limited to this example. For example, an index of an upper layerand the importance level have any relationship. Specifically, in theforegoing, the setting unit 133 may calculate that the importance levelis high for a frame containing data of the base layer, and calculatethat the importance level is low for a frame containing data of theenhancement layer. The present technology is not limited to thisexample. For example, the setting unit 133 may calculate that theimportance level is low for a frame containing data of the base layer,and calculate that the importance level is high for a frame containingdata of the enhancement layer. The same applies to other methods ofcalculating the importance level.

Also, in the foregoing, an example has been described in which thecommunication system 1 is a system compliant with wireless LAN or acommunication standard similar to this. The present technology is notlimited to this. For example, the communication system 1 may be a systemcompliant with other communication standards.

Also, in the foregoing, an example has been described in which a mainentity which performs retransmission control is the base station 100.The present technology is not limited to this. For example, a wirelessterminal, such as a smartphone or the like, may be a main entity whichperforms retransmission control. Also, in addition to the communicationform in which the base station 100 is a center of wirelesscommunication, the communication system 1 may be, for example, in apeer-to-peer (P2P) type communication form. In this case, a wirelessterminal which performs P2P communication may perform retransmissioncontrol.

Also, the embodiments and variations of the present disclosure may becombined as appropriate.

The series of control processes carried out by each apparatus describedin the present specification may be realized by software, hardware, or acombination of software and hardware. Programs that compose suchsoftware may be stored in advance for example on a storage medium(non-transitory medium) provided inside or outside each of theapparatus. As one example, during execution, such programs are writteninto RAM (Random Access Memory) and executed by a processor such as aCPU.

Note that it is not necessary for the processing described in thisspecification with reference to the flowchart to be executed in theorder shown in the flowchart. Some processing steps may be performed inparallel. Further, some of additional steps can be adopted, or someprocessing steps can be omitted.

In addition, the effects described in the present specification aremerely illustrative and demonstrative, and not limitative. In otherwords, the technology according to the present disclosure can exhibitother effects that are evident to those skilled in the art along with orinstead of the effects based on the present specification.

Additionally, the present technology may also be configured as below.

(1)

A wireless communication apparatus including:

a wireless communication unit configured to perform wirelesscommunication with a terminal apparatus;

a communication control unit configured to control multicasttransmission performed by the wireless communication unit; and

a setting unit configured to set a threshold for determining whether ornot it is necessary for the communication control unit to perform aretransmission process, on the basis of information about reception of areception acknowledgment response corresponding to the multicasttransmission from the terminal apparatus.

(2)

The wireless communication apparatus according to (1),

wherein the threshold is a threshold related to a number of the terminalapparatuses which have transmitted back the reception acknowledgmentresponse corresponding to the multicast transmission.

(3)

The wireless communication apparatus according to (1),

wherein the threshold is a threshold related to a proportion of theterminal apparatuses which have transmitted back the receptionacknowledgment response corresponding to the multicast transmission tothe terminal apparatuses which are a destination of the multicasttransmission.

(4)

The wireless communication apparatus according to (1),

wherein the threshold is a threshold related to a number of times ofretransmission of a frame which has been subjected to the multicasttransmission.

(5)

The wireless communication apparatus according to any one of (1) to (4),

wherein the information about reception of the reception acknowledgmentresponse is information indicating an importance level of a transmittedframe for which reception of the reception acknowledgment response hasresulted in failure, and

wherein the setting unit calculates the importance level on the basis ofinformation about a multicast frame for which reception of thecorresponding reception acknowledgment response has resulted in failure.

(6)

The wireless communication apparatus according to (5),

wherein the setting unit calculates the importance level on the basis ofan index of an upper layer related to data contained in the multicastframe.

(7)

The wireless communication apparatus according to (6),

wherein the index of the upper layer contains information indicating ahierarchical level of encoding of the data encoded by a hierarchicalencoding technique.

(8)

The wireless communication apparatus according to (6) or (7),

wherein the index of the upper layer contains information indicatingwhether or not the data contains at least any one of video and audio.

(9)

The wireless communication apparatus according to any one of (6) to (8),

wherein the index of the upper layer contains information indicating adependence relationship between the data and other data.

(10)

The wireless communication apparatus according to any one of (6) to (9),

wherein the index of the upper layer contains information indicatingwhether or not the data contains a time stamp.

(11)

The wireless communication apparatus according to any one of (6) to(10),

wherein the index of the upper layer contains information indicatingwhether or not the data contains a protocol header of the upper layer.

(12)

The wireless communication apparatus according to any one of (5) to(11),

wherein the setting unit calculates the importance level on the basis ofa transmission setting which has been used in transmission of themulticast frame.

(13)

The wireless communication apparatus according to (12),

wherein the transmission setting contains a setting for performingtransmission using a bundle of a plurality of frequency channels.

(14)

The wireless communication apparatus according to any one of (5) to(13),

wherein the setting unit calculates the importance level on the basis ofinformation about a media access control (MAC) layer of the multicastframe.

(15)

The wireless communication apparatus according to (14),

wherein the information about the MAC layer contains informationindicating a type of the multicast frame.

(16)

The wireless communication apparatus according to (14) or (15),

wherein the information about the MAC layer contains informationindicating a data amount of the multicast frame.

(17)

The wireless communication apparatus according to any one of (1) to(16), further including:

a retransmission method determination unit configured to determine atransmission method in the retransmission process performed by thecommunication control unit, on the basis of information about theterminal apparatus which has failed to receive the receptionacknowledgment response corresponding to the multi cast transmission.

(18)

The wireless communication apparatus according to any one of (1) to(17), further including:

a retransmission timing determination unit configured to determine atiming at which the communication control unit is to perform theretransmission process.

(19)

A wireless communication method for use in a wireless communicationapparatus which performs wireless communication with a terminalapparatus, the method including:

controlling multicast transmission using a processor; and

setting a threshold for determining whether or not it is necessary toperform a retransmission process, on the basis of information aboutreception of a reception acknowledgment response corresponding to themulticast transmission from the terminal apparatus.

(20)

A program for causing a computer to function as:

a wireless communication unit configured to perform wirelesscommunication with a terminal apparatus;

a communication control unit configured to control multicasttransmission performed by the wireless communication unit; and

a setting unit configured to set a threshold for determining whether ornot it is necessary for the communication control unit to perform aretransmission process, on the basis of information about reception of areception acknowledgment response corresponding to the multicasttransmission from the terminal apparatus.

REFERENCE SIGNS LIST

-   1 communication system-   100 base station-   110 wireless communication unit-   120 storage unit-   130 control unit-   131 communication control unit-   133 setting unit-   135 retransmission method determination unit-   137 retransmission timing determination unit-   200 wireless terminal

1. A wireless communication apparatus comprising: a wirelesscommunication unit configured to perform wireless communication with aterminal apparatus; a communication control unit configured to controlmulticast transmission performed by the wireless communication unit; anda setting unit configured to set a threshold for determining whether ornot it is necessary for the communication control unit to perform aretransmission process, on the basis of information about reception of areception acknowledgment response corresponding to the multicasttransmission from the terminal apparatus.
 2. The wireless communicationapparatus according to claim 1, wherein the threshold is a thresholdrelated to a number of the terminal apparatuses which have transmittedback the reception acknowledgment response corresponding to themulticast transmission.
 3. The wireless communication apparatusaccording to claim 1, wherein the threshold is a threshold related to aproportion of the terminal apparatuses which have transmitted back thereception acknowledgment response corresponding to the multicasttransmission to the terminal apparatuses which are a destination of themulticast transmission.
 4. The wireless communication apparatusaccording to claim 1, wherein the threshold is a threshold related to anumber of times of retransmission of a frame which has been subjected tothe multicast transmission.
 5. The wireless communication apparatusaccording to claim 1, wherein the information about reception of thereception acknowledgment response is information indicating animportance level of a transmitted frame for which reception of thereception acknowledgment response has resulted in failure, and whereinthe setting unit calculates the importance level on the basis ofinformation about a multicast frame for which reception of thecorresponding reception acknowledgment response has resulted in failure.6. The wireless communication apparatus according to claim 5, whereinthe setting unit calculates the importance level on the basis of anindex of an upper layer related to data contained in the multicastframe.
 7. The wireless communication apparatus according to claim 6,wherein the index of the upper layer contains information indicating ahierarchical level of encoding of the data encoded by a hierarchicalencoding technique.
 8. The wireless communication apparatus according toclaim 6, wherein the index of the upper layer contains informationindicating whether or not the data contains at least any one of videoand audio.
 9. The wireless communication apparatus according to claim 6,wherein the index of the upper layer contains information indicating adependence relationship between the data and other data.
 10. Thewireless communication apparatus according to claim 6, wherein the indexof the upper layer contains information indicating whether or not thedata contains a time stamp.
 11. The wireless communication apparatusaccording to claim 6, wherein the index of the upper layer containsinformation indicating whether or not the data contains a protocolheader of the upper layer.
 12. The wireless communication apparatusaccording to claim 5, wherein the setting unit calculates the importancelevel on the basis of a transmission setting which has been used intransmission of the multicast frame.
 13. The wireless communicationapparatus according to claim 12, wherein the transmission settingcontains a setting for performing transmission using a bundle of aplurality of frequency channels.
 14. The wireless communicationapparatus according to claim 5, wherein the setting unit calculates theimportance level on the basis of information about a media accesscontrol (MAC) layer of the multicast frame.
 15. The wirelesscommunication apparatus according to claim 14, wherein the informationabout the MAC layer contains information indicating a type of themulticast frame.
 16. The wireless communication apparatus according toclaim 14, wherein the information about the MAC layer containsinformation indicating a data amount of the multicast frame.
 17. Thewireless communication apparatus according to claim 1, furthercomprising: a retransmission method determination unit configured todetermine a transmission method in the retransmission process performedby the communication control unit, on the basis of information about theterminal apparatus which has failed to receive the receptionacknowledgment response corresponding to the multicast transmission. 18.The wireless communication apparatus according to claim 1, furthercomprising: a retransmission timing determination unit configured todetermine a timing at which the communication control unit is to performthe retransmission process.
 19. A wireless communication method for usein a wireless communication apparatus which performs wirelesscommunication with a terminal apparatus, the method comprising:controlling multicast transmission using a processor; and setting athreshold for determining whether or not it is necessary to perform aretransmission process, on the basis of information about reception of areception acknowledgment response corresponding to the multicasttransmission from the terminal apparatus.
 20. A program for causing acomputer to function as: a wireless communication unit configured toperform wireless communication with a terminal apparatus; acommunication control unit configured to control multicast transmissionperformed by the wireless communication unit; and a setting unitconfigured to set a threshold for determining whether or not it isnecessary for the communication control unit to perform a retransmissionprocess, on the basis of information about reception of a receptionacknowledgment response corresponding to the multicast transmission fromthe terminal apparatus.